For many years KEF were the exclusive manufacturers of the LS5/1A monitor for the BBC, a high performance system that demanded meticulous production control. The Reference Series Model 5/1AC was a KEF designed, active system based on the same speaker, and it found use in many of the new independent radio stations of the day.

The system was a two-way with active crossover network, internal 75W power amplifiers for each drive unit, thermal overload protection circuit and a three position bass equalization.